Argon-mercury discharge tube



Aug Z, W28, lfiSQZTH R. a MACHLETT ARGON MERCURY DISCHARGE TUBE Filed July 9, 1927 INVENTOR.

v ATTORNEY Patented Aug. 7, i928.

HTE gTA I return are cures.

RAYMOND ROBERT MAGHLETT, OF NEW YORK, N. Y., ASSIGNOR TO RAINBOW LIGHT,

- ENG, A CORPORATION OF NEW YORK.

ARGON-MERCURY Application filed July 9,

My present invention relates to an improved discharge tube in which a rarefied gas acts as the conducting medium, said tube being provided with interior electrodes.

With my improved tube 1 make use of pure argon gas as the conducting atmosphere preferably at a pressure of about millimeters of mercury. The electrical characteristics of argon are exceptionally favor- 10 able for the purpose; it is even more readily conducting than neon. The luminosity of neon, however, is better and therefore with my improved tube 1 avail myself of the lu minous efficiency of mercury vapor by which a very beautiful blue light can be secured if the tube is of transparent glass. By using glass of amber color and in other ways known to the art, various shades of green may be secured.

Heretofore it has been roposed to secure blue and green effects in uminous tubes by the use of mercury vapor in a luminous tube employing neon. In such a tube under iavorable conditions entirely satisfactory blue and green effects can be secured but a neonmercury tube is extremel sensitive to changes in temperature. ith such a tube if the ambient temperature drops below 40 Fahrenheit, portions of the tube assume the characteristic red neon color, causing the tube to present a spotty appearance. This is a serious disadvantage especially if the tube is used as an electric sign. If the ambient temperature is still further re duced, for instance, down to 309 F. or lower, the tube may become entirely red, showing the characteristic color of neon and giving no indication to the eye of the mercury spectrum at all. This is due to the fact that ENE the temperature of the tube also decreases, the vapor tension of the mercury vapor likewise decreases and when this vapor; is

. used with neon the electrical conditions within the tube are such at low temperatures that the decreased amount of mercury vapor no longer plays apart in the production of light in the tube.

I am aware of the fact that Cooper Hewitt in the early days proposed the use of rare gases including argon in his well known mercury vapor lamp, simply for the purpose of starting the same, but so far as I know, the commercial mercury vapor tub es have always depended upon short c1rcu1t-1ng in as the ambient temperature decreases and DISCHARGE TUBE.

192?. Serial m. 204,479.

order to effect this result. With my improved tube the argon is not utilized for effecting the starting of the tube nor is the mercury vapor utilized to an appreciable extent for. conduct-ion. My invention is strictly an argon tube and the desirable characteristics of argon are depended upon for conduction, the mercury vapor being used to impart its characteristic radiation to the emitted light.

I find that with a mixture ofargon gas and mercury vapor the ener values required to produce ionization an radiation of both gases are nearly the same. Under the conditions in an argon tube containing mercury vapor this is more nearly the case than with any other practical combination of which,

I have knowledge and is certainly more nearly the case than with the combination of neon and mercury vapor. With argon as'the main conducting medium, the condi tions of energy between its ions are of ap proximately the optimum values to produce ionization and radiation from the mercury vapor and thus even though a very small amount of mercury vapor be resent its characteristic radiation is still 0 served in the light emitted by the combination.

Lamps employing this combination and properly recessed as I shall hereafter describe, wi I retain their characteristic clear blue or green color even-when the ambient temperature may be' so 'low as zero degrees Fahrenheit, and even lower.

I find in practice that the best results are secured when the mercuryvapor is produced from the glass walls which are saturated with the mercury evenly and uniformly along the tube. If this precaution is not observed, the lamp is likely to become striated and exhibit sections of varying light intensity along its length. This particular diflicult-y is due, I believe, to the fact that the glass contains a good deal of free alkali metal which will distill out of the glass and accumulate on the interior walls during the heating of the tube in its formation. This accumulation of alkali metal on the glass walls is, of course, very minute cury in such an amalgam possesses a very low vapor tension. Therefore unless the alkali metal is substantially eliminated there will be present in the tube throughout its length more or less isolated sections of amalgam in which the mercury vaportension is very low and which tends to give the striated effect above .referred to. It is thus desirable to eliminate as much of the free alkali in the glass to be used in the manufacture of these tubes as possible before the formation of the tube. This is best accomplished by placing the glass in a-pickling bath consisting of a weak acid solution (for example, 2% hydrofluoric acid) for severil days before using the glass to form the tu e. i

It is also important after the lamp has been formed to allow the glass to become thoroughly saturated with mercury along. its entire length before the tube is ready to be used. This second precaution should be car ried out with sufficient thoroughness, as I will hereafter describe, to permit the complete saturation of any-alkali metal deposit which may exist in the tube in spite of the pickling process.

Assuming that the tube has been suitabl pickled, is in its 'final form or shape so ar as its contour is concerned, and is provided with the-usual interior electrodes, it is preferably attached to a high vacuum difiusion pump system of any ordinary construction which will include an arrangement for admitting pure argon to the tube at the proper pressure. This of course is well known practice in the art. The preferred pressure is in the neighborhood of 10 millimeters of mercury.

During the pumping, the lamp is maintained within an ordinary oven heated by gas or in any other usual way and is heated at a temperature as high as glass will stand without collapsing. Preferably high-melting boro-silicon glass is used Which maintains its form through exhaustion u to a temperature as high as 450 Centigrade. Also with this glass the difficulties due to the presence of alkali metal are minimized. During the pumping and baking process it is necessary to eliminate impurities from the electrodes, since the proper operation of the lamp depends upon the ideal characteristics of pure argon gas which may be seriously distorted and disturbed by the presence of even slight amounts of impurities. This purification of the electrodes is preferably effected by passing through the tubes during the exhaustion process a cur rent of very much higher value than is ordinarily employed and preferably sufficient to heat the electrodes red hot. I prefer to use graphite for the electrode material and. to heat theelctrodes by the currents referred to a temperature of approximately 1,000? C. during the pumping operation. During this purification process the current in the tube is conducted by the residual ai'r therein and also by reason of carbon dioxide and other gas or gases evolved from the electrodes. The purifying current is now discontinued and the electrodes are allowed to cool, the pumping going on until all traces of carbon dioxide are removed and until the desired degree of evacuation has been secured.

When the processing of the lamp has been best results. In this drawing:

Fig. 1 shows a section of a well known baking ovenwith a tube therein in process of formation, and

Fig. 2 is a longitudinal elevation of the tube at. a later stage of its process.

The oven is shown at l and is supplied with gas or other heating means, the tube is indicated at 2, interior electrodes are shown at 3, and the wires for supporting the tube in the oven are shown at 44.

The tube is formed with a small bulbular attachment or sidetube 5 as shown, from which a tube 7 leads to the lamp and a tube 8.1eads to the outside of the oven, the end havinga bulb 9 containing a small quantity of very pure mercury. The attachment for admitting the argon is not shown. Any approved practice in this respect may be followed.

When the state of processing has been loo reached in which the tube contains pure ar- Y gon at the desired pressure, some of-the mercury in the bulb 9 is distilled over and accumulates in the bulb 5 as shown in Fig. 2. Of course at this time the oven is cool so that the mercury vapor will immediately condense in the bulb 5. The pipes 7 and 8 are now tipped off asshown in Fig. 2. Here the tube has been thoroughly purified as well as the electrodes, itcont'ains argon at the desired pressure, and the side tube 5 is still in place containing the mercury.

It is desirable, as a matter of precaution,

25 before tipping oif tubes 7 and 8 to operate j i scribed, it will be necessary to continue the operation of the pump until all impurities have disappeared in the argon spectrum, before allowing the mercury in the side bulb 5 to enter the tube for the reason that purification of the tube cannot be carried out after the mercury has been admitted to it. Of course, should repumping be necessary to remove unexpected impurities a further quantity of argon will have to be admitted to brin the pressure to the desired point. A num er of scavengings of the tube may be carried out in this way, although ordinarily it will not be necessary.

Mercury from the side tube 5 may be admitted to the lamp by simply tilting up the. side tube and allowing the mercury to flow into the lamp after which it will be dis tributed mechanically through the same as uniformly as possible. ()f course the amount of mercury thus introduced will be extremely small. The side tube 5 is now tipped 01f and it then becomes important to carry out further operations by which the glass walls of the lamp will be saturated evenly and uniformly with mercury to result in the successful operation of the lamp even at extremely low ambient temperatures. v Preferably I apply lengthwise of the tube small cooling surfaces which may conveniently be copper bars having a width in the neighborhood of 2 centimeters, spaced about 20 centimeters apart. As a matter of fact the tube may be conveniently supported upon acopper grid composed of such bars suitably spaced apart so that the points of' contact between the glass walls and the copper bars will constitute cooling areas from which heat will be dissipated by conduction through the bars. I now operate the lamp with the current slightly in excess of its rated value so as to cause the lamp to 'become somewhat warm and this current will cause the mechanically distributed mercury to be vaporized within the tube. This vapor in turn will tend to condense upon'the cooling surfaces and, form small mercury mirrors on the glass walls of a diameter of about. 2 square centimeters, spaced about 20 centimeters apart, although, of course, the diameter of these mirrors and their spacing are not important, the essential object being to uniformly distribute throughout the length of the tube a series of mercury mirrors which in practice will act as sources of supply for the operation of the tube.

and to otherwise manipulate it without affecting the uniform distribution of the mercury throughout the tube in the form of small mirrors on the glass walls as described.

The formation of the mercury throughout the tube in this way afi'ords a quick and ready method of distribution thereof. If the small mercury mirrors were not formed and the mercury was simply allowed to diffuse throughout the tube a great deal of time would be lost in the manufacture of the tubes. By the method described a tube is formed which, when it operates, results in an immediate and uniform evolution of mercury va or throughout the tube so as to give a uni orm color throughout without striated or spotty portions. The subsequent operations of the tube result in the condensation of the mercury vapor upon the entire tube Walls so that eventually the mercury mirrors become less conspicuous and may in time entirely diappear.

Having now described m invention, what I claim as new therein an desire to secure by Letters Patent, is as follows:

1. An improved luminous tube containing an atmosphere. of rarefied argon and mercury vapor, the latter being evolved uniformly from the surface of the glass walls of the tube.

2. An improved luminous tube comprising a tubular glass receptacle, the walls of which are free of alkali metal and said tube containing rarefied argon and mercury vapor.

3. An improved luminous. tube containing an atmosphere of rarefied argon and mercury vapor, the latter being evolved from small mercu mirrors distributed lengthwise of the tu e.

4. .An improved luminous tube provided with interior electrodes and containing rarefied argon and mercury vapor, the latter' being evolved from small mercury mirrors distributed lengthwise of .the tube.

-RAYMOND ROBERT CHLETT- 

